U.S. patent number 5,911,162 [Application Number 08/880,035] was granted by the patent office on 1999-06-08 for capacitive pressure transducer with improved electrode support.
This patent grant is currently assigned to MKS Instruments, Inc.. Invention is credited to John A. Denner.
United States Patent |
5,911,162 |
Denner |
June 8, 1999 |
Capacitive pressure transducer with improved electrode support
Abstract
The disclosed pressure transducer assembly includes metallic
body, a diaphragm, a metallic plate, an insulator, and a conductor.
The body defines an interior cavity. The diaphragm is mounted in
the body and divides the interior cavity into a first chamber and a
second chamber. A portion of the diaphragm flexes in a first
direction in response to a pressure in the first chamber being
greater than a pressure in the second chamber, and that portion of
the diaphragm flexes in a second direction opposite the first
direction in response to the pressure in the second chamber being
greater than the pressure in the first chamber. The metallic plate
is fixed to the metallic body in one of the first and second
chambers. The insulator is also disposed in that chamber and is
fixed to the metallic plate. The conductor is disposed on the
insulator. The diaphragm and the conductor are characterized by a
capacitance. The capacitance is representative of a difference
between the pressures in the first and second chambers.
Inventors: |
Denner; John A. (Lynn, MA) |
Assignee: |
MKS Instruments, Inc. (Andover,
MA)
|
Family
ID: |
25375383 |
Appl.
No.: |
08/880,035 |
Filed: |
June 20, 1997 |
Current U.S.
Class: |
73/718;
361/283.4; 73/724 |
Current CPC
Class: |
G01L
19/0618 (20130101); G01L 9/0072 (20130101) |
Current International
Class: |
G01L
9/00 (20060101); G01L 009/12 () |
Field of
Search: |
;73/724,718
;361/283.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
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1 282 302 |
|
Nov 1968 |
|
DE |
|
1 497 212 |
|
Jan 1978 |
|
GB |
|
2188155 |
|
Sep 1987 |
|
GB |
|
Other References
Baratron.RTM. Absolute Pressure Transmitters 400 Series,
.COPYRGT.1996 MKS Instruments, Inc., Andover, MA. .
Baratron.RTM. General Purpose Absolute Pressure Transducers, 1993
MKS Instruments, Inc..
|
Primary Examiner: Felber; Joseph L.
Attorney, Agent or Firm: Hale and Dorr LLP
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
The present invention is related to subject matter disclosed in
copending U.S. patent application Ser. No. 08/748,820, entitled
"Pressure Sensor", which was invented by the inventor of the
present invention and which has been assigned to the assignee of
the present invention.
Claims
What is claimed is:
1. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a plate, said plate being fixed to said body in said first
chamber;
(D) an insulator disposed in said first chamber, said insulator
being fixed to said plate, a first portion of said plate overlying
a first portion of said insulator, said first portion of said plate
being spaced apart from said first portion of said insulator;
(E) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
2. An assembly according to claim 1, wherein said plate and said
body are metallic.
3. An assembly according to claim 2, wherein said plate is welded
to said body.
4. An assembly according to claim 1, wherein said insulator
comprises a ceramic material.
5. An assembly according to claim 1, wherein only a central portion
of said insulator is fixed to said plate and a gap is provided
between an outer perimeter of said insulator and said body.
6. An assembly according to claim 1, further comprising a spacer
disposed between said insulator and said plate.
7. An assembly according to claim 1, wherein said plate comprises a
spacer, said spacer being disposed proximal said insulator.
8. An assembly according to claim 1, further including an
electrically conductive feedthrough, one end of said feedthrough
being disposed in said first chamber and another end of said
feedthrough being external to said body, said feedthrough extending
through apertures in said plate and said body, said feedthrough
being electrically connected to said conductor and being
electrically insulated from said plate and from said body.
9. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a plate fixed to said body in said first chamber, said plate
comprising a first material;
(D) an insulator disposed in said first chamber, said insulator
comprising a second material different from said first
material;
(E) a fastener fixing a central portion of said insulator to said
plate;
(F) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
10. An assembly according to claim 9, wherein said fastener
comprises a screw.
11. An assembly according to claim 9, wherein said fastener
comprises a rivet.
12. An assembly according to claim 9, wherein said fastener
comprises an adhesive.
13. An assembly according to claim 9, wherein said plate rigidly
supports said insulator.
14. An assembly according to claim 9, wherein said body and said
plate are metallic.
15. An assembly according to claim 14, wherein said plate is welded
to said body.
16. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a plate fixed to said body in said first chamber;
(D) an insulator disposed in said first chamber;
(E) a spacer disposed between said plate and said insulator;
(F) a fastener fixing a central portion of said insulator and said
spacer to said plate;
(G) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
17. An assembly according to claim 16, wherein said fastener
comprises a screw.
18. An assembly according to claim 16, wherein said fastener
comprises a rivet.
19. An assembly according to claim 16, wherein said fastener
comprises an adhesive.
20. An assembly according to claim 16, wherein said body and said
plate are metallic.
21. An assembly according to claim 20, wherein said plate is welded
to said body.
22. A pressure transducer assembly comprising:
(A) a metallic body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a metallic member fixed to at least a portion of said metallic
body in said first chamber;
(D) an insulator disposed in said first chamber, said insulator
being fixed to said metallic member;
(E) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
23. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a conductor disposed in one of said first and second chambers,
said conductor and said diaphragm being characterized by a
capacitance, said capacitance being representative of a difference
between said pressures in said first and second chambers;
(D) a resilient element disposed in said one chamber, said
resilient element providing a force that biases said conductor away
from said diaphragm.
24. An assembly according to claim 23, further including an
insulator, said conductor being disposed on said insulator.
25. An assembly according to claim 24, said resilient element
contacting a portion of said body and a portion of said
insulator.
26. An assembly according to claim 23, said body comprising a
sidewall and a cover, a lower portion of said sidewall being fixed
to a portion of said diaphragm, a portion of said cover being fixed
to an upper portion of said sidewall, said sidewall, said cover,
and said diaphragm defining said first chamber.
27. An assembly according to claim 26, further including an
insulator, said conductor being disposed on said insulator.
28. An assembly according to claim 27, said resilient element
biasing said insulator away from said diaphragm towards said
cover.
29. An assembly according to claim 28, a portion of said resilient
element contacting said sidewall.
30. An assembly according to claim 28, further including a
fastener, said fastener holding a portion of said resilient element
in contact with said cover.
31. An assembly according to claim 28, said cover rigidly
preventing said insulator from moving in a direction away from said
diaphragm.
32. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a metallic plate fixed to said body in said first chamber;
(D) an insulator disposed in said first chamber, said insulator
being fixed to said plate;
(E) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
33. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a plate welded to said body in said first chamber;
(D) an insulator disposed in said first chamber, said insulator
being fixed to said plate;
(E) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
34. A pressure transducer assembly comprising:
(A) a body defining an interior cavity;
(B) a diaphragm mounted in said body and dividing said interior
cavity into a first chamber and a second chamber, a portion of said
diaphragm flexing in a first direction in response to a pressure in
said first chamber being higher than a pressure in said second
chamber, said portion of said diaphragm flexing in a second
direction opposite said first direction in response to said
pressure in said second chamber being higher than said pressure in
said first chamber;
(C) a plate fixed to said body in said first chamber, said plate
comprising a first material;
(D) an insulator disposed in said first chamber, said insulator
being fixed to said plate, said insulator comprising a second
material different from said first material;
(E) a conductor disposed on said insulator, said conductor and said
diaphragm being characterized by a capacitance, said capacitance
being representative of a difference between said pressures in said
first and second chambers.
Description
BACKGROUND OF THE INVENTION
The present invention relates to capacitive pressure transducers.
More specifically, the present invention relates to an improved
electrode support for use with capacitive pressure transducers.
FIG. 1A shows a partially sectional side view of an assembled prior
art capacitive pressure transducer assembly 100. FIG. 1B shows an
exploded sectional side view of transducer assembly 100. For
convenience of illustration, FIGS. 1A and 1B, as well as other
figures in the present disclosure, are not drawn to scale. U.S.
Pat. No. 4,823,603 discloses a capacitive pressure transducer
assembly of the general form of transducer assembly 100. U.S. Pat.
Nos. 5,020,377 and 4,785,669 also disclose capacitive pressure
transducers relevant to the present disclosure.
Briefly, transducer assembly 100 includes a body that defines a
first sealed interior chamber 110, and a second sealed interior
chamber 112. Chambers 110 and 112 are isolated from one another by
a relatively thin, flexible, conductive diaphragm 120. As will be
discussed in greater detail below, diaphragm 120 is mounted so that
it flexes, or deflects, in response to pressure differentials in
chambers 110 and 112. Transducer assembly 100 provides a parameter
that is indicative of the amount of diaphragm flexure and this
parameter is therefore indirectly indicative of the differential
pressure. The parameter provided by transducer assembly 100
indicative of the differential pressure is the electrical
capacitance between diaphragm 120 and an electrode 130.
Transducer assembly 100 includes a P.sub.-- x cover 140 and a
P.sub.-- x body 150 (as will be discussed below, the term "P.sub.--
x" refers to an unknown pressure). FIG. 2A shows a top view of
P.sub.-- x body 150. P.sub.-- x body 150 has a tubular shape and
defines a central interior aperture 152 (shown in FIG. 2A and
indicated by lines 153 in FIG. 1B). The upper surface of P.sub.-- x
body 150 is stepped and provides a shoulder 154 that extends around
the perimeter of aperture 152. P.sub.-- x body 150 also includes a
lower surface 156. The P.sub.-- x cover 140 is a circular metallic
sheet and is provided with a pressure tube 142 that defines a
central aperture 144. The P.sub.-- x cover 140 is rigidly affixed
to the lower surface 156 of P.sub.-- x body 150 (e.g., by welding).
Diaphragm 120 is normally a thin, circular, flexible sheet of
conductive material (e.g., stainless steel). As stated above, FIGS.
1A and 1B are not drawn to scale, and diaphragm 120 is normally
much thinner than illustrated in comparison to the other components
of transducer assembly 100. Diaphragm 120 contacts shoulder 154 of
P.sub.-- x body 150 as indicated in FIG. 1A. The outer perimeter of
diaphragm 120 is normally welded to P.sub.-- x body 150 to rigidly
hold the outer perimeter of diaphragm 120 to the shoulder 154 of
P.sub.-- x body 150.
P.sub.-- x cover 140, P.sub.-- x body 150, and diaphragm 120
cooperate to define the interior sealed chamber 110. P.sub.-- x
cover 140 defines the bottom, P.sub.-- x body 150 defines the
sidewalls, and diaphragm 120 defines the top of chamber 110. Fluid
in tube 142 may flow through aperture 144, and through central
aperture 152 (shown in FIG. 2A) into chamber 110. So, fluid in tube
142 is in fluid communication with the lower surface of diaphragm
120.
Transducer assembly 100 also includes a P.sub.-- r body 160 and a
P.sub.-- r cover 170 (as will be discussed below, the term
"P.sub.-- r" refers to a reference pressure). FIG. 2B shows a top
view of P.sub.-- r body 160. P.sub.-- r body 160 has a tubular
shape and defines a central aperture 162 (shown in FIG. 2B and
indicated by lines 263 in FIG. 1B). The upper surface of P.sub.-- r
body 160 is stepped and provides a lower shoulder 164 and an upper
shoulder 166. The lower shoulder 164 extends around the perimeter
of aperture 162, and the upper shoulder 166 extends around the
perimeter of lower shoulder 164. P.sub.-- r body 160 also includes
a lower surface 168 opposite to shoulders 164, 166. The lower
surface 168 of P.sub.-- r body 160 is rigidly affixed to the upper
surface of the outer perimeter of diaphragm 120 (e.g., by welding).
The P.sub.-- r cover 170 is a circular metallic sheet and is
provided with a pressure tube 172 which defines a central aperture
174. P.sub.-- r cover 170 is rigidly affixed to P.sub.-- r body 160
(e.g., by welding) so that the outer perimeter of P.sub.-- r cover
170 is in contact with upper shoulder 166 of P.sub.-- r body
160.
P.sub.-- r cover 170, P.sub.-- r body 160, and diaphragm 120
cooperate to define the interior sealed chamber 112. Diaphragm 120
defines the bottom, P.sub.-- r body 160 defines the sidewalls, and
P.sub.-- r cover 170 defines the top of chamber 112. Fluid in tube
172 may flow through aperture 174, and through central aperture 162
(shown in FIG. 2B) into chamber 112. So, fluid in tube 172 is in
fluid communication with the upper surface of diaphragm 120. As
will be discussed below, electrode 130 is housed in, and does not
interfere with the fluid flow in, chamber 112.
Electrode 130 is normally fabricated from a non-conducting (or
insulating) ceramic block and has a cylindrical shape. FIG. 2C
shows a bottom view of electrode 130. The lower surface of
electrode 130 is stepped and includes a central face 135 and a
shoulder 136 that extends around the outer perimeter of central
face 135. Electrode 130 also defines an aperture 132 (shown in FIG.
2C and indicated by lines 133 in FIG. 1B). Electrode 130 further
includes a relatively thin conductor 134 that is deposited (e.g.,
by electroplating) onto the central face 135. Conductor 134 is
explicitly shown in FIGS. 1B and 2C, and for convenience of
illustration, conductor 134 is not shown in FIG. 1A. Electrode 130
is clamped between P.sub.-- r cover 170 and the lower shoulder 164
of the P.sub.-- r body 160 as shown in FIG. 1A. Aperture 132 (shown
in FIG. 2C) in electrode 130 permits fluid to freely flow through
electrode 130 between the upper surface of diaphragm 120 and
pressure tube 172. Clamping the electrode 130 to the P.sub.-- r
body 160 holds the conductor 134 in spaced relation to the
diaphragm 120. Electrode 130 is normally positioned so that the
space between conductor 134 and diaphragm 120 is relatively small
(e.g., on the order of 0.0002 meters).
Conductor 134 and diaphragm 120 form parallel plates of a capacitor
138. As is well known, C=Ae/d, where C is the capacitance between
two parallel plates, A is the common area between the plates, e is
a constant based on the material between the plates (e=1 for
vacuum), and d is the distance between the plates. So, the
capacitance provided by capacitor 138 is a function of the distance
between diaphragm 120 and conductor 134. As the diaphragm 120
flexes up and down, in response to changes in the pressure
differential between chambers 110 and 112, the capacitance provided
by capacitor 138 also changes. At any instant in time, the
capacitance provided by capacitor 138 is indicative of the
instantaneous differential pressure between chambers 110 and 112.
Known electrical circuits (e.g., a "tank" circuit characterized by
a resonant frequency that is a function of the capacitance provided
by capacitor 138) may be used to measure the capacitance provided
by capacitor 138 and to provide an electrical signal representative
of the differential pressure.
Transducer assembly 100 includes an electrically conductive
feedthrough 180 to permit measurement of the capacitance provided
by capacitor 138. One end 182 of feedthrough 180 contacts electrode
130. Feedthrough 180 extends through an aperture in P.sub.-- r
cover 170 so that the other end 184 of feedthrough 180 is external
to transducer assembly 100. The aperture in P.sub.-- r cover 170
through which feedthrough 180 extends is sealed, for example by a
melted glass plug 185, to maintain the pressure in chamber 112 and
to electrically insulate feedthrough 180 from P.sub.-- r cover 170.
Feedthrough 180 is electrically connected to conductor 134.
Electrode 130 normally includes an electroplated through hole (not
shown) to permit electrical connection between conductor 134 (on
the bottom surface of electrode 130) and end 182 of feedthrough 180
which contacts the top surface of electrode 130. So, feedthrough
180 provides electrical connection to one plate of capacitor 138
(i.e., conductor 134). Since diaphragm 120 is welded to P.sub.-- r
body 160, the P.sub.-- r body 160 provides electrical connection to
the other plate of capacitor 138 (i.e., diaphragm 120). So, the
capacitance provided by capacitor 138 may be measured by
electrically connecting a measuring circuit (not shown) between
P.sub.-- r body 160 and end 184 of feedthrough 180. In practice,
the body of transducer assembly 100 is normally grounded, so the
capacitance provided by capacitor 138 may be measured simply by
electrically connecting the measuring circuit to end 184 of
feedthrough 180.
Conductor 134 is normally disposed in a circular "ring-like"
configuration on the lower surface of electrode 130 (as indicated
in FIG. 2C). Further, some prior art pressure transducers include
more than one conductor disposed on electrode 130 and a
corresponding number of feedthroughs to electrically connect to the
conductors. Such transducers provide at least two capacitors: a
first capacitor formed by diaphragm 120 and one conductor on
electrode 130 and a second capacitor formed by diaphragm 120 and
another conductor on electrode 130. As is known, providing multiple
capacitors in this fashion can be used to advantageously provide
temperature compensation for the transducer.
In operation, transducer assembly 100 is normally used as an
absolute pressure transducer. In this form, chamber 112 is normally
first evacuated by applying a vacuum pump (not shown) to pressure
tube 172. After chamber 112 has been evacuated, tube 172 is then
sealed, or "pinched off" to maintain the vacuum in chamber 112.
This creates a "reference" pressure in chamber 112. Although a
vacuum is a convenient reference pressure, it is also known to use
other pressures as the reference pressure. Since the pressure in
chamber 112 is a known or reference pressure, the components used
to construct chamber 112 (i.e., P.sub.-- r body 160 and P.sub.-- r
cover 170) are referred to as P.sub.-- r components (i.e.,
"reference pressure" components). After the reference pressure has
been established in chamber 112, the pressure tube 142 is then
connected to a source of fluid (not shown) to permit measurement of
the pressure of that fluid. Coupling the pressure tube 142 in this
fashion delivers the fluid, the pressure of which is to be
measured, to chamber 110 (and to the lower surface of diaphragm
120). Since the pressure in chamber 110 is unknown, or is to be
measured, the components used to construct chamber 110 (i.e.,
P.sub.-- x cover 140 and P.sub.-- x body 150) are referred to as
P.sub.-- x components (i.e., "unknown pressure" components). The
center of diaphragm 120 flexes up or down in response to the
differential pressure between chambers 110 and 112. Transducer
assembly 100 permits measurement of the amount of flexure of the
diaphragm and thereby permits measurement of the pressure in
chamber 110 relative to the known pressure in chamber 112.
Transducer assembly 100 can of course also be used as a
differential pressure transducer. In this form, pressure tube 142
is connected to a first source of fluid (not shown) and pressure
tube 172 is connected to a second source of fluid (not shown).
Transducer assembly 100 then permits measurement of the difference
between the pressures of the two fluids.
One problem with transducer assembly 100 relates to the spacing
between conductor 134 and diaphragm 120. In operation of transducer
assembly 100, the diaphragm 120 of course flexes up and down
thereby changing the spacing between diaphragm 120 and conductor
134. However, for transducer assembly 100 to provide a consistently
accurate pressure reading, it is important to provide a constant
nominal spacing between diaphragm 120 and conductor 134. So for a
particular pressure differential, it is important to insure that
the distance between diaphragm 120 and conductor 134 is always the
same. The distance between diaphragm 120 and conductor 134 for a
particular pressure differential between chambers 110 and 112 may
be referred to as the "nominal distance". When manufacturing large
numbers of transducer assemblies 100, it is important to
consistently provide the same nominal distance between conductor
134 and diaphragm 120. Further, in any one unit of transducer
assembly 100, it is important to insure that the nominal distance
remains constant and does not vary over time.
Prior art transducer assembly 100 includes a resilient element 192
for maintaining a constant nominal distance. Resilient element 192
is squeezed between P.sub.-- r cover 170 and the top of electrode
130. The lower shoulder 164 of P.sub.-- r body 160 supports
shoulder 136 of electrode 130. Since P.sub.-- r cover 170 is welded
to P.sub.-- r body 160, resilient element 192 provides a spring
force that pushes down on electrode 130 and holds electrode 130 in
a fixed position relative to P.sub.-- r body 160. Resilient element
192 is often implemented using a "wave washer" (i.e., a metallic
O-ring type washer that has been bent in one or more places in
directions perpendicular to the plane of the ring). Resilient
element 192 provides a relatively large spring force (e.g., on the
order of one hundred pounds) so as to hold electrode 130 in a
stable position.
Although transducer assembly 100 holds the electrode 130 securely,
the nominal distance between conductor 134 and diaphragm 120 can
vary by small amounts over time in response to, for example,
mechanical or thermal shock. As those skilled in the art will
appreciate, elements that are held in place by compression, such as
electrode 130, can exhibit small amounts of movement (sometimes
referred to as "creep") over time. This creep can sometimes change
the nominal distance and thereby adversely affect the accuracy of
the transducer assembly 100. Overpressure conditions can also cause
unwanted movement of electrode 130. During normal operation of
transducer assembly 100, diaphragm 120 will never contact electrode
130. However, large pressures in chamber 110 beyond the normal
operating range of transducer assembly 100 (i.e., overpressure),
can cause diaphragm 120 to contact electrode 130 and slightly
compress resilient element 192. When the overpressure condition
dissipates and diaphragm 120 returns to a normal operating
position, resilient element 192 re-expands and reseats electrode
130. Sometimes the new position of electrode 130 will be slightly
different than the original position prior to the overpressure
condition. Such changes in position can cause shifts in the nominal
distance and adversely affect the accuracy of the transducer
assembly 100.
It is therefore an object of the present invention to provide a
pressure transducer assembly with an improved mounting for the
electrode.
SUMMARY OF THE INVENTION
The invention provides an improved mounting for an electrode in a
pressure transducer. The mounting provides improved stability for
the electrode.
In one aspect, the invention provides an improved pressure
transducer assembly. The assembly includes a body, a diaphragm, a
plate, an insulator, and a conductor. The body defines an interior
cavity. The diaphragm is mounted in the body and divides the
interior cavity into a first chamber and a second chamber. A
portion of the diaphragm flexes in a first direction in response to
a pressure in the first chamber being greater than a pressure in
the second chamber, and that portion of the diaphragm flexes in a
second direction opposite the first direction in response to the
pressure in the second chamber being greater than the pressure in
the first chamber. The plate is fixed to the body in one of the
first and second chambers (e.g., by welding or screws). The
insulator is also disposed in that chamber and is fixed to the
plate. The conductor is disposed on the insulator. The diaphragm
and the conductor are characterized by a capacitance. The
capacitance is representative of a difference between the pressures
in the first and second chambers.
In another aspect, the invention provides a transducer assembly
that includes a body, a diaphragm, a conductor, and a resilient
element. The resilient element is disposed in the body and provides
a force that biases the conductor away from the diaphragm.
Still other objects and advantages of the present invention will
become readily apparent to those skilled in the art from the
following detailed description wherein several embodiments are
shown and described, simply by way of illustration of the best mode
of the invention. As will be realized, the invention is capable of
other and different embodiments, and its several details are
capable of modifications in various respects, all without departing
from the invention. Accordingly, the drawings and description are
to be regarded as illustrative in nature, and not in a restrictive
or limiting sense, with the scope of the application being
indicated in the claims.
BRIEF DESCRIPTION OF THE FIGURES
For a fuller understanding of the nature and objects of the present
invention, reference should be made to the following detailed
description taken in connection with the accompanying drawings in
which the same reference numerals are used to indicate the same or
similar parts wherein:
FIG. 1A shows a partially sectional side view of a prior art
assembled transducer assembly;
FIG. 1B shows an exploded sectional side view of the assembly shown
in FIG. 1A;
FIG. 2A shows a top view of the P.sub.-- x body shown in FIGS.
1A-1B;
FIG. 2B shows a top view of the P.sub.-- r body shown in FIGS.
1A-1B;
FIG. 2C shows a bottom view of the electrode shown in FIGS.
1A-1B;
FIG. 3A shows a partially sectional side view of a capacitive
pressure transducer assembly constructed according to the present
invention;
FIG. 3B shows an exploded sectional side view of the assembly shown
in FIG. 3A;
FIGS. 4A and 4B show sectional side and bottom views, respectively,
of a preferred embodiment of the electrode shown in FIGS.
3A-3B;
FIG. 5 shows an exploded sectional side view of another pressure
transducer assembly constructed according to the present
invention;
FIG. 6 shows a bottom view of the P.sub.-- r cover shown in FIG.
5;
FIG. 7 shows an exploded sectional side view of yet another
pressure transducer assembly constructed according to the present
invention; and
FIG. 8 shows an exploded sectional side view of still another
pressure transducer assembly constructed according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 3A shows a partially sectional side view of an assembled
transducer assembly 200 constructed according to the present
invention. FIG. 3B shows an exploded sectional side view of
transducer assembly 200. In the preferred embodiment, many
components used to construct transducer assembly 200 are the same,
or are similar to, components used in prior art transducer assembly
100. More specifically, transducer assembly 200 includes the
P.sub.-- x cover 140, P.sub.-- x body 150, diaphragm 120, P.sub.--
r body 160, and P.sub.-- r cover 170 components that were used in
prior art transducer assembly 100. However, rather than electrode
130, transducer assembly 200 includes improved electrode 230.
Further, transducer assembly 200 eliminates the need for, and
preferably does not include, resilient element 192.
As in prior art transducer assembly 100, P.sub.-- x cover 140,
P.sub.-- x body 150, and diaphragm 120 are connected together to
form sealed interior chamber 110 on one side of the diaphragm. Also
as in prior art transducer assembly 100, diaphragm 120, P.sub.-- r
body 160, and P.sub.-- r cover 170 are connected together to form
sealed interior chamber 112 on the other side of the diaphragm.
Electrode 230 includes a metallic plate 232, a spacer 234, and a
ceramic (or other form of insulative) plate 236. Spacer 234 is
positioned between metallic plate 232 and ceramic plate 236. A
fastener (not shown) such as a screw, a rivet, or an adhesive,
holds metallic plate 232, spacer 234, and ceramic plate 236
securely together. In some embodiments, spacer 234 is formed as an
integral part of metallic plate 232 and in other embodiments,
spacer 234 is provided as a separate and distinct component.
Metallic plate 232 and P.sub.-- r body 160 are rigidly fixed
together, for example by welding, so that the outer perimeter of
metallic plate 232 contacts shoulder 164. The lower surface of
ceramic plate 236 is provided in conventional fashion with an
electrical conductor 238 (shown in FIG. 3B and not in FIG. 3A).
Fixing metallic plate 232 to shoulder 164 securely positions
conductor 238 in spaced relation to diaphragm 120. Conductor 238
and diaphragm 120 form a capacitor 240. The nominal distance
between conductor 238 and diaphragm 120 may be controlled, for
example, by selecting a spacer 234 with a desired thickness.
Transducer assembly 200 includes an electrically conductive
feedthrough 280 for electrically connecting to conductor 238. One
end 282 of feedthrough 280 contacts the upper surface of ceramic
plate 236. Feedthrough 280 extends through apertures in metallic
plate 232 and P.sub.-- r cover 170 and the other end 284 of
feedthrough 280 is external to transducer assembly 200. As with
prior art transducer assembly 100, the aperture in P.sub.-- r cover
170 through which feedthrough 280 extends is sealed (e.g., with
glass plug 185) to maintain pressure in chamber 112 and to
electrically insulate feedthrough 280 from P.sub.-- r cover 170.
Metallic plate 232 defines an aperture, indicated by lines 233 in
FIG. 3B, through which feedthrough 280 extends. This aperture is
larger than feedthrough 280 so that feedthrough 280 does not
contact metallic plate 232. This electrically insulates feedthrough
280 from metallic plate 232 and also equalizes pressure on both
sides of plate 232 to insure that the pressure in tube 172 is
communicated to the upper surface of diaphragm 120. The lower end
282 of feedthrough 280 is electrically connected to conductor 238.
Feedthrough 280 is electrically connected to one plate (i.e.,
conductor 238) of capacitor 240, and P.sub.-- r body 160 is
electrically connected to the other plate (i.e., diaphragm 120) of
capacitor 240.
In preferred embodiments, feedthrough 280 does not structurally
support ceramic plate 236. Rather, plate 236 is supported by being
connected to metallic plate 232 which is rigidly fixed to P.sub.--
r body 160. As shown more clearly in FIGS. 5, 7, and 8, the
electrical feedthrough may include a conductive pin and a
conductive coil spring. The pin is rigidly fixed to the P.sub.-- r
cover and the coil spring extends from the pin to the ceramic
electrode. While the spring electrically connects to the conductor
disposed on the ceramic electrode, the spring does not provide
structural support for the electrode.
Unlike prior art electrode 130 (shown in FIGS. 1A and 1B),
electrode 230 of transducer assembly 200 is not held in place by
spring forces produced by compressing a resilient element. Rather,
metallic plate 232 of electrode 230 is rigidly fixed to the
P.sub.-- r body 160 (e.g., by welding or screws). A fastener
rigidly holds ceramic plate 236 (and conductor 238) of electrode
230 to metallic plate 232 via spacer 234. This substantially
reduces the tendency for electrode 230 to move, or creep, over time
and thereby improves the performance of transducer assembly 200.
The stability of electrode 230 in response to mechanical and
thermal shock as well as to overpressure conditions is improved.
Since metallic plate 232 is rigidly fixed to P.sub.-- r body 160,
overpressure conditions do not tend to cause any appreciable
movement of electrode 230.
In preferred embodiments of transducer assembly 200, ceramic plate
236 is mounted by fixing only a central portion of the ceramic
plate 236 to the metallic plate 232. The outer perimeter of ceramic
plate 236 is spaced apart from, and is not in contact with, the
P.sub.-- r body 160. This stands in contrast with prior art
transducer assembly 100 wherein the entire outer perimeter of
ceramic electrode 130 was supported by the P.sub.-- r body (and
resilient element 192). This improves the stability of electrode
230.
Transducer assembly 200 is also simpler to manufacture than prior
art transducer assembly 100. When manufacturing prior art
transducer assembly 100, the step or shoulder 136 in electrode 130
must be precisely machined. The need for this shoulder is
eliminated in transducer assembly 200 thereby reducing critical
feature tolerances.
Electrode 230 is preferably sized to fit as a replacement part into
the P.sub.-- r body 160 of prior art transducer assemblies. Tests
conducted on prior art transducer assembly 100 and assembly 200
(where assembly 200 was constructed by substituting electrode 230
for prior art electrode 130) indicate that transducer assembly 200
provides improved performance.
FIGS. 4A and 4B show sectional side and bottom views, respectively,
of a preferred embodiment of electrode 230. In this embodiment,
metallic plate 232, spacer 234, and ceramic plate 236 each define a
central bore hole 242. A portion of bore hole 242 in metallic plate
232 is preferably threaded to permit a screw 244 (shown in FIG. 4B)
to hold metallic plate 232, spacer 234, and ceramic plate 236
together. Ceramic plate 236 also preferably defines a depression
246 that is wider than, and that connects to, bore hole 242 to
permit counter sinking of screw 244. It is desirable to provide for
countersinking of screw 244 in this manner to prevent any portion
of screw 244 from entering the space between electrical conductor
238 and diaphragm 120. In other embodiments, a rivet or an adhesive
may be used in place of screw 244. In yet another embodiment, one
end of screw (or bolt) 244 extends through bore hole 244 and a nut
(not shown) is threaded onto that end and cooperates with screw 244
to hold the spacer 234 and plates 232, 236 together. In this
embodiment, bore hole 242 may or may not be threaded. FIG. 4A also
shows the aperture 248 defined in metallic plate 232 through which
feedthrough 280 passes.
In preferred embodiments, P.sub.-- x cover 140, P.sub.-- x body
150, P.sub.-- r body 160, P.sub.-- r cover 170, metallic plate 232,
and spacer 234 are all fabricated from the same metal (e.g.,
Inconnel .RTM., a nickel, iron, and chromium alloy ). Ceramic plate
236 is preferably fabricated from alumina or Fosterite (i.e.,
Magnesium Silicate).
For convenience of description, transducer assembly 200 has been
described as having a single conductor disposed on electrode 230.
However, those skilled in the art will appreciate that in other
embodiments, transducer assembly 200 may include one or more
conductors disposed on electrode 230. Further, those skilled in the
art will appreciate that plate 232 need not contact shoulder 164 of
the P.sub.-- r body 160 and could instead be fixed in other places
to P.sub.-- r body 160 or P.sub.-- r cover 170. Still further, in
other embodiments, plate 232 could be eliminated and ceramic (or
insulative) plate 236 could be supported by another form of
metallic structure rigidly fixed to the P.sub.-- r body or P.sub.--
r cover.
FIG. 5 shows an exploded sectional side view of another embodiment
of a transducer assembly 300 constructed according to the present
invention. Transducer assembly 300 includes diaphragm 120 mounted
between P.sub.-- r body 160 and a unified P.sub.-- x body/cover
340. The outer perimeter of diaphragm 120 is fixed to P.sub.-- x
body/cover 340 to form the first interior sealed chamber 110 on one
side of diaphragm 120. P.sub.-- x body/cover 340 is provided with
pressure tube 142 to permit coupling a source of pressurized gas
(not shown) to chamber 110. P.sub.-- r body 160 is also fixed to
the outer perimeter of diaphragm 120 on the side of diaphragm 120
opposite to chamber 110.
Transducer assembly 300 also includes an improved P.sub.-- r cover
370 and annular resilient elements 390. FIG. 6 shows a bottom view
of P.sub.-- r cover 370. As shown in FIGS. 5 and 6, the lower
surface of P.sub.-- r cover 370 is stepped and defines a central
face 372, a first shoulder 373, a second shoulder 374, a third
shoulder 375, and a fourth shoulder 376. The first shoulder 373
extends around at least a portion of the perimeter of the central
face 372; the second shoulder 374 extends around at least a portion
of the perimeter of the first shoulder 373; the third shoulder 375
extends around at least a portion of the perimeter of the second
shoulder 374; and the fourth shoulder 376 extends around at least a
portion of the perimeter of the third shoulder 375. In the
illustrated embodiment, central face 372 is circular and shoulders
373-376 are annular and are concentric with central face 372. The
first and second shoulders 373, 374 are separated by a vertical
face 378.
When transducer assembly 300 is assembled, the fourth shoulder 376
of P.sub.-- r cover 370 contacts the upper shoulder 166 of the
P.sub.-- r body 160. The third shoulder 375 preferably contacts, or
nearly contacts, the lower shoulder 164 of the P.sub.-- r body 160.
In the illustrated embodiment, the second shoulder 374 is recessed
from the third shoulder 375 (so that the second shoulder 374 is
disposed further away from diaphragm 120 than is the third shoulder
375), the first shoulder 373 is recessed from the second shoulder
374, and the central face 372 is recessed from the first shoulder
373.
Transducer assembly 300 also includes an electrode 330. Electrode
330 has the same general form as electrode 130, however, the outer
perimeter of electrode 330 is smaller than that of electrode 130.
Electrode 330 is generally cylindrical. The lower surface of
electrode 330 is stepped and provides a central face and a shoulder
336 that extends around the perimeter of the central face.
Electrode 330 also includes a conductor (not shown) deposited onto
the central face of the lower surface.
When transducer assembly 300 is assembled, the P.sub.-- r cover 370
is rigidly attached (e.g., by welding) to P.sub.-- r body 160. The
P.sub.-- r cover 370, the P.sub.-- r body 160, and the diaphragm
120 cooperate to form the second sealed interior chamber 112
opposite to the first interior chamber 110. Although not
illustrated, those skilled in the art will appreciate that P.sub.--
r cover 370 may be provided with a pressure tube to provide access
to chamber 112. An outer portion of resilient element 390 rests on
the lower shoulder 164 of P.sub.-- r body 160. When transducer
assembly 300 is assembled, the third shoulder 375 of the P.sub.-- r
cover and the lower shoulder 164 of the P.sub.-- r body preferably
squeeze the outer perimeter of the resilient element 390. The inner
perimeter of the resilient element 390 contacts the shoulder 336 of
electrode 330 and provides a force that tends to push the electrode
330 away from the diaphragm 120. More specifically, the resilient
element 390 pushes the electrode so that the upper surface of
electrode 330 contacts and is supported by the first shoulder 373
of the P.sub.-- r cover. Further, the vertical face 378 of the
P.sub.-- r cover 370 restricts movement of electrode 330 in
directions parallel to the diaphragm 120. The P.sub.-- r cover 370
is preferably sized so that the electrode 330 snugly fits within
the vertical face 378 that separates the first and second shoulders
373, 374.
In the illustrated embodiment, transducer assembly 300 includes two
electrical feedthroughs that extend through P.sub.-- r cover 370
and make electrical contact with two conductors (not shown)
disposed on the lower surface of electrode 330. Each of the
feedthroughs 380 are surrounded by insulators 381 that may be made
for example from glass. Insulators 381 electrically insulate
feedthroughs 380 from the P.sub.-- r cover 370 and also maintain
pressure inside the second interior cavity 112.
The P.sub.-- r cover 370 rigidly supports electrode 330 and
prevents electrode 330 from moving in a direction away from
diaphragm 120 (e.g., in response to an overpressure condition).
Resilient element 390 provides a relatively small force (e.g., on
the order of ten pounds) that prevents motion of electrode 330
towards diaphragm 120. The relatively small force applied by
resilient element 390 maintains contact between the upper surface
of electrode 330 and the first shoulder 373 of P.sub.-- r cover
370. P.sub.-- r cover 370 thereby rigidly supports the electrode
330 and rigidly prevents the electrode 330 from moving in a
direction away from the diaphragm 120.
Prior art transducer assembly 100 used resilient element 192 to
provide a relatively large force (e.g., 100 pounds) to push
electrode 130 down towards the diaphragm to attempt to rigidly hold
electrode 130 in place. In contrast to the prior art, in transducer
assembly 300, the resilient element 390 provides a relatively small
force (e.g., ten pounds) that biases the electrode 330 upwards away
from the diaphragm and the P.sub.-- r cover 370 rigidly prevents
the electrode 330 from moving in a direction away from diaphragm
120. Transducer assembly 300 thereby advantageously maintains a
substantially constant nominal spacing between the diaphragm 120
and the conductors (not shown) of electrode 330.
FIG. 7 shows an exploded side view of another embodiment of a
pressure transducer assembly 400 constructed according to the
present invention. Transducer assembly 400 preferably includes the
same P.sub.-- x body/cover 340 and the same P.sub.-- r cover 370
that were used in assembly 300 (shown in FIG. 5). However, rather
than P.sub.-- r body 160 and electrode 330 which were used in
transducer assembly 300, transducer assembly 400 includes a
cylindrical P.sub.-- r body 460 and a cylindrical electrode 430.
P.sub.-- r body 460 is simpler than P.sub.-- r body 160 because
P.sub.-- r body 460 includes only a single shoulder 466 (rather
than two shoulders). Those skilled in the art will appreciate that
providing each shoulder requires a separate machining step. So,
since P.sub.-- r body 460 includes only a single shoulder it costs
less to produce than P.sub.-- r body 160. Similarly, electrode 430
is simpler than electrode 330. As discussed above, electrode 330
provides a shoulder 336. Rather than a shoulder, electrode 430
provides a groove 432 in at least a portion of the perimeter of
electrode 430. Those skilled in the art will appreciate that it is
less expensive to provide a groove such as groove 432 than it is to
provide a shoulder such as shoulder 336 in a ceramic component such
as electrode 430. So electrode 430 costs less to produce than
electrode 330.
When assembled, P.sub.-- r cover 370 is fixed to P.sub.-- r body
460 so that shoulder 376 of the P.sub.-- r cover 370 contacts the
shoulder 466 of the P.sub.-- r body. Rather than being supported by
a portion of the P.sub.-- r body, the outer perimeter of resilient
element 490 is fixed to the fourth shoulder 375 of the P.sub.-- r
cover 370 for example by screws 492 or other fasteners such as
rivets or adhesives. The inner perimeter of resilient element 490
contacts electrode 430 inside of groove 432 and applies a force
that biases electrode 430 against the first shoulder 373 of the
P.sub.-- r body 370. Resilient element 490 and P.sub.-- r cover 370
provide improved support for electrode 430 similar to that provided
in transducer assembly 300 (shown in FIG. 5). However, rather than
use a shoulder of the P.sub.-- r body to support the outer
perimeter of the resilient element, the outer perimeter of the
resilient element is fixed to the P.sub.-- r cover. This
advantageously eliminates the need for the extra shoulder in the
P.sub.-- r body.
FIG. 8 shows a sectional side view of yet another pressure
transducer assembly 500 constructed according to the present
invention. Transducer assembly 500 includes a tubular P.sub.-- r
support 590. P.sub.-- r support 590 defines a central aperture 592.
The lower surface of P.sub.-- r support 590 is stepped and defines
a first shoulder 593, a second shoulder 594, and a third shoulder
595. The first shoulder 593 extends around the perimeter of
aperture 592. The second shoulder extends around the perimeter of
the first shoulder 593. The third shoulder 595 extends around the
perimeter of the second shoulder 594. The first and second
shoulders 593, 594 are separated by a vertical face 596. In the
illustrated embodiment, the central aperture 592 is circular; the
first, second, and third shoulders 593, 594, 595 are annular; and
the first, second, and third shoulders 593, 594, 595 are concentric
with the central aperture 592.
When transducer assembly 500 is assembled, the lower surface of the
outer perimeter of resilient element 390 rests on shoulder 164 of
the P.sub.-- r body 160. The third shoulder 595 of the P.sub.-- r
support 590 rests on the upper surface of the outer perimeter of
resilient element 390. The inner perimeter of the resilient element
390 biases the shoulder 336 of electrode 330 upwards so that
electrode 330 remains confined by the first shoulder 593 and the
vertical face 596 of the P.sub.-- r support 590. The P.sub.-- r
cover 170 is fixed to the P.sub.-- r body 160 so that the lower
surface of P.sub.-- r cover 170 contacts the upper shoulder 166 of
the P.sub.-- r body 160. Resilient element 192 is squeezed between
P.sub.-- r cover 170 and the upper surface of the P.sub.-- r
support 590 and exerts a downward force on the P.sub.-- r support
590.
Prior art transducer assembly 100 used metallic resilient element
192 to directly bias the ceramic electrode in a downwards
direction. In contrast, in transducer assembly 500 the metallic
resilient element biases the P.sub.-- r support 590 rather than the
ceramic electrode. So, in transducer assembly 500, all the
components that are exposed to the relatively large force provided
by resilient element 192 (i.e., P.sub.-- r support 590, resilient
element 390, P.sub.-- r body 160, and P.sub.-- r cover 170) may be
fabricated from the same material (e.g., metal). Ceramic electrode
330 is supported by P.sub.-- r body 590 rather than by resilient
element 192. Transducer assembly 500 therefore provides an improved
more stable support for the electrode.
Since certain changes may be made in the above apparatus without
departing from the scope of the invention herein involved, it is
intended that all matter contained in the above description or
shown in the accompanying drawing shall be interpreted in an
illustrative and not a limiting sense. As an example, the electrode
430 (shown in FIG. 7) could be used as the electrode in variations
of assembly 300 (shown in FIG. 5) or in assembly 500 (shown in FIG.
8). Similarly, the electrode 330 (shown in FIG. 5) could be used in
a variation of assembly 400 (shown in FIG. 7). As another example,
the metallic plate 232 (shown in FIGS. 3A-3B) of electrode 230
could be fixed to the P.sub.-- r cover rather than to the P.sub.--
r body. As yet another example, while annular conductors have been
illustrated, those skilled in the art will appreciate that various
forms and numbers of conductors may be disposed on the electrodes
to form capacitors with the diaphragm. As yet another example, in
the preferred embodiment of electrode 230 (shown in FIGS. 3A and
3B), only the central portion of ceramic plate 236 is fixed to
metallic plate 232. Those skilled in the art will appreciate
however that this is a preferred embodiment and not a limitation of
the invention. In other embodiments, other portions of insulating
plate 236 may be fixed to metallic plate 232. Still further, in
other embodiments, portions or the entire perimeter of insulating
plate 236 may contact the P.sub.-- r body 160.
* * * * *